The present invention relates to a susceptor for use in the microwave cooking of food, and more particularly to such a susceptor which is both edible and biodegradable, as well as a method of using the same.
The susceptors for microwave cooking available in the commercial markets include metallized film or paper sheet laminations containing glue. These commercially available susceptors are not fully acceptable since they are not entirely safe as there is a possibility that the metal or glue utilized therein could release toxic compounds during or after microwave heating, thereby contaminating the food being cooked. Further, the commercially available susceptors are not attractive from an ecological point of view since they are not biodegradable. Accordingly, the need remains for a safe susceptor, preferably biodegradable and edible.
The susceptor of the present invention is intended to be used in a conventional manner--that is, intimately contacted with the food to be cooked in order to form an assembly, the assembly heated in a microwave oven to cook the food, and then the assembly dismantled, with the susceptor being separated from the cooked food. Nonetheless, the edible nature of such a susceptor remains important for a variety of reasons. First, the edible nature ensures that there will not be any metal or glue to release toxic compounds during or after microwave heating. Second, the user of the susceptor is assured that, even if a portion of the susceptor adheres to the food being cooked or the susceptor bursts or breaks during the course of cooking, the food does not become contaminated and inedible. For these purposes, the term "edible" as used herein and in the claims encompasses, in addition to materials which are conventionally thought of as edible, small amounts of paper and plastic, which, although not particularly palatable, may be ingested without adverse effects.
Various susceptors have been proposed for use in microwave cooking in order to increase the sensible heat level immediately adjacent the food being cooked. The proposed susceptors include polypropylene-coated wax paper or polyhydroxyl alcohol-containing substrates. Glycerine and propylene glycol are examples of the polyhydroxyl alcohols which are high lossy materials that can be employed to convert a portion of the microwave energy impacting thereon into sensible heat. See, for example, U.S. Pat. Nos. 4,882,184 and 4,968,865. The highest temperature achievable with a propylene glycol susceptor is 185.degree. C., and the highest temperature achievable with a glycerine susceptor is 290.degree. C. These temperatures are, however, the temperatures achievable in the alcohols, not the temperature which is experienced by the food being cooked. Due to the heat-transfer resistance of whatever material contains the alcohol and the air gap between the alcohol-containing film and the food being cooked, the temperature at the contact surface of the food is substantially less than the temperature of the alcohol itself and, typically less than 135.degree. C. Thus the known alcohol-based susceptors simply lack sufficient effectiveness for many applications where a higher temperature is desired, and especially where a high temperature is desired in a very limited time (time being of the essence since quick cooking is a main attraction of the microwave cooking system). The heating rates of glycerine and polypropylene glycol are not high enough to be compatible with the commercially available metallized film or paper laminated susceptors.
In order to provide a benchmark for satisfactory performance of a lossy material, it was determined that 25 grams of a lossy material in a 50 milliliter glass beaker should be heatable to at least 200.degree. C. within 40 seconds by 900 watts of microwave energy in 1.1 cubic foot oven. The 900 watt 1.1 cubic foot oven represents the capacity of a common household microwave oven, 40 seconds represents a satisfactorily short microwave cook time (depending on the size of the foodstuff), and 200.degree. C. provides sufficient sensible heat for general susceptor purposes, including browning. In other words, the lossy material should enable the food to achieve a surface temperature of at least 135.degree. C. in microwave heating. For comparative purposes, glycerine by itself as a lossy material, under the test conditions noted above, is heatable to only 160.degree. C. within 40 seconds.
Accordingly, it is an object of the present invention to provide a susceptor for use in the microwave cooking of food which contains a lossy material heatable to at least 200.degree. C. in a common household microwave oven.
Another object is to provide such a susceptor which in a preferred embodiment is biodegradable.
A further object is to provide such a susceptor which in a preferred embodiment is edible.
It is also an object of the present invention to provide such a susceptor which is economical to manufacture and simple and safe to use.
It is another object to provide a method of microwave cooking using such a susceptor.